The central role of tRNA in protein synthesis includes the steps by which nucleic acid code works are translated into amino acids. Amino acids are enzymatically attached to tRNA and thus adapted to recognize mRNA codons. Protein chain initiation can involve modification of aminoacyl-tRNA. The amount, kind or activity of tRNA varies during cell differentiation or changes in metabolic state (sporulation, tumor development, virus infection and hormonal treatment). The necessary information for all these functions lies in the primary structure of the tRNA molecule. This project will attempt to correlate tRNA structure with the various biological and regulatory functions of the molecule. A set of genetically produced related tRNA species will be selected for specific changes in biological function. Determination of the nucleotide sequence of these tRNAs in conjunction with biochemical studies will allow correlation of changes in structure to changes in specific functions of this important cell constituent.